Allied|Blythe House, Blythe Road — the building where Max is told his wife may be a spy

The worst scene in the film happens in a corridor. Max Vatan is called in by his own service and told, without ceremony, that his wife is suspected of working for the Germans, and that if it is true he will be required to shoot her himself.

Those intelligence-headquarters sequences were filmed at Blythe House, a vast Edwardian block on Blythe Road behind Olympia in west London. It was built between 1899 and 1903 as the headquarters of the Post Office Savings Bank, and it looks exactly like the kind of place a wartime bureaucracy would occupy: red brick and Portland stone, a symmetrical façade, small windows in long institutional rows, a central pediment over the entrance.

For decades afterwards it held reserve collections for the V&A, the Science Museum and the British Museum — millions of objects in rooms the public almost never saw. Those collections have been moving out to purpose-built stores, and the building's next chapter is still being written.

You cannot walk in. What you can do is stand on Blythe Road and look up. The scale is the thing: floor after identical floor of windows, each one a room where a decision about someone's life could be taken by a person you would never meet. The film did not need to invent an atmosphere of impersonal machinery. It only had to point a camera at this façade.